The present invention relates to a joint arrangement for gas turbine engine casings, particularly gas turbine engine fan casings and more particularly to an improved casing joint arrangement for use within or forming a part of the gas turbine engine blade containment assembly.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor which is enclosed by a generally cylindrical, or frustoconical, fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
However, in the event that a blade becomes detached, the blade strikes the metal casing and a significant load is imparted from the main impact region of the metal casing to a flanged interface with an intake casing or rear fan casing.
It is normal practice to transfer the impact loads along the metal casing to the flanged interface joint with the intake or rear fan casing. The flanged interface is bolted together with an array of circumferentially spaced bolts. Under impact by a released fan blade, the flanged joint between the metal casing and the intake or rear fan casing has a tendency to open thus permitting an unwanted and substantial degree of movement of the joint. To counter this the flanged joint is a substantial structure and is therefore of considerable weight. Furthermore it is a requirement for the bolts to resist the considerable shear force between casings and therefore the bolts are also of substantial number, size and weight. Nevertheless it is known that the integrity of the bolted flange joint can be lost and debris from a blade off event pass through the flanged joint.
Accordingly the present invention seeks to provide a novel gas turbine engine casing joint which is of less weight, deforms less, and absorbs more energy and transfers less impact load to the intake or rear fan casing than has previously been the case.
Accordingly the present invention provides a joint assembly for limiting an extension of the joint in the direction of a load path derived from an impact comprising: a first member and a second member each having overlapping portions arranged generally parallel to one another and secured together via securing means disposed through corresponding holes defined therein; wherein one of the overlapping portions further defines, sequentially in the direction of extension, a shear neck, a pocket and a catcher portion; so that in the event of a worst case impact load the securing means shears through the shear neck and the pocket and is arrested by the catcher portion, thereby the extension of the joint assembly may be limited and the joint assembly remains integral.
Preferably, one overlapping portion is configured as a tongue portion and the other overlapping portion is configured as a groove portion, the tongue portion engages the groove portion in a conventional manner.
Preferably, the pocket comprises a membrane but alternatively the pocket comprises an aperture.
Alternatively, the pocket comprises at least one further shear neck.
Preferably, the membrane is of a constant thickness, but alternatively the membrane may be of variable thickness and the membrane increases in thickness between the shear neck and the catcher portion.
Alternatively pocket is substantially semi-circular in configuration about the hole and the pocket comprises at least one radially aligned spoke.
Alternatively, an energy absorbing insert is disposed to the pocket.
Preferably, a sealing means is provides to substantially prevent fluid flow through the joint.
Alternatively, contact surfaces comprise a means for enhancing friction.
Alternatively, the tongue portion comprises a discrete tongue portion and the groove portion comprises a groove and a radial slot, the slot so disposed that it extends the groove locally and axially rearward, the tongue portion arranged to engage the groove and the discrete tongue portion arranged to engage the radial slot.
Preferably the tongue portion and groove portion of the foregoing paragraph comprise a plurality of corresponding discrete tongue portions and slots.
Preferably, the tongue portion and the groove portion are annular.
Preferably, a gas turbine engine rotor blade fan casing assembly comprises a joint assembly as claimed in any of the above paragraphs.
Preferably, the fan casing assembly comprises a metal casing and a rear fan casing, the casing assembly comprising the first member and the rear fan casing comprising the second member.
Alternatively, the metal casing is any one of a group comprising a fan containment casing and a core engine casing.
Preferably, the impact is derived from a released rotor blade striking the containment casing during operation of the engine.
Preferably, a plurality of joint assemblies are circumferentially disposed about the fan casing assembly.
Preferably, at least one additional pocket is disposed between each joint assembly.